Quick Answer: A used shipping container rust inspection works through three critical zones, following the IICL container inspection standards the trade uses. The three zones to read on any used box are the roof (pooling, pinhole light, seam separation), the door frame and gasket channel (where weather penetrates first), and the steel cross-members under the floor (Corten patina is normal, perforation is not). Surface rust on side walls is wire-brush, primer, paint, and forget. Active rust around weld seams, soft floor you can push a screwdriver through, or daylight through the roof or corner castings is a walk-away. We inspect every container at our 4 Brantford yards before it goes on the customer row, and we will read the rust with you on any 20ft or 40ft you point at before money changes hands. 30+ years operating, 4.9 stars on 124+ Google reviews. 1-3 day delivery Ontario-wide from our Brantford yards.
In This Field Guide
- What is the difference between Corten patina and active rust?
- How do you inspect a container roof for rust?
- Is surface rust on container walls a problem?
- What should you check on container doors and gaskets?
- How do you inspect a container floor and cross-members?
- What do corner castings and the CSC plate tell you?
- What are the deal-breakers that make Christian walk away?
- What container rust is fixable, and what is not?
- How does Van Blanc run a rust inspection at the Brantford yard?
- Frequently asked questions
Reading time: about 12 minutes. This checklist sits under our complete walkthrough for buying a second-hand box and pairs with our first-time buyer primer and our breakdown of Canadian grades and sizes for the condition definitions behind every term below.
What Is the Difference Between Corten Patina and Active Rust?
Corten patina is the stable, tightly bonded oxide layer that weathering steel forms over one to three years, and it protects the steel beneath. Active rust is porous, flakes off in scales, and traps moisture so corrosion drives inward. The fingernail test separates them: patina resists a scrape, while active rust scales off and shows pitted steel underneath.
Most rust questions at the yard start the same way. A buyer points at a brown patch and asks if the container is rusted out. Nine times in ten the answer is no, that is the steel doing what it is supposed to do. A rust inspection is knowing which is in front of you.
Shipping containers are built from Corten, a low-alloy weathering steel formulated to form a tight adherent oxide layer (patina) once it gets wet and dries. After roughly 1.5 to 3 years of outdoor exposure that patina blocks further oxygen and water from reaching the metal beneath. References: Total Materia on weathering steel and HZ Containers on the container application.
Active corrosion looks similar at a glance and behaves nothing alike. Active rust is porous, flakes in laminated scales, and holds moisture against the steel underneath so corrosion drives inward. The fingernail test catches the difference: patina resists a scrape and stays put; active rust comes off in scales, shows lighter steel or pitting underneath, and leaves a wet-looking residue on your thumb.
The factor that splits the two is wet-dry cycling. Continuous wetness (roof that pools, gasket that never drains, casting parked in a puddle) defeats the weathering chemistry and starts active corrosion. Our inspection concentrates on the zones where water sits longest.
Christian LeBlanc, second-generation operator, 19 years on the yard: “First thing I do with a buyer is teach the fingernail test. Take a nail to the worst-looking brown patch. If you cannot scrape anything off and your nail stays clean, that is patina and the box is fine. If a brown scale comes off and the steel under it is pitted, we have to decide how deep it goes. The whole inspection is a series of those decisions.”
How Do You Inspect a Container Roof for Rust?
A container roof inspection runs in three passes: a ground-level look up both long sides, an inside look straight up for daylight pinholes, and a top pass walking the roof with a wire brush and screwdriver. The roof is the single most important rust zone on any used container. Sea-going boxes spend years stacked exposed to weather and salt air, and the roof catches all of it. Roofs are thinner-gauge than side walls (1.6 mm versus 2 mm), so any active corrosion has a head start eating through.
Three passes. Ground level first: walk both long sides and look up. A roof that has lost camber, sagged in the middle, or has standing-water pools after recent rain flags as higher-risk. Inside next: stand inside with the doors closed, look straight up, let your eyes adjust. Any pinhole rust-through shows as a bright pinpoint of daylight. One or two pinholes in a 40-footer roof can be welded in a one-day repair (cost range from YES Containers). Six or eight pinholes in the same square metre is the start of a roof-replacement conversation.
Top pass: ladder up, walk the roof with a wire brush, a thin screwdriver, and a flashlight. Push the screwdriver tip into the seam welds, the perimeter where the roof meets the top rail, and any spot that sagged or pooled from below. Tip pushes through: perforation. Tip slides off hard: surface scale on intact steel.
Seam separation is the failure buyers miss most often. The roof is welded from multiple narrow steel panels along long seams. Decades of thermal cycling and stack-load flexing can micro-crack those seams. Give-away: a stripe of staining on the inside ceiling running parallel to the seam. See it and the roof will leak in the first heavy Ontario thaw whether you see a pinhole today or not.
Is Surface Rust on Container Walls a Problem?
Surface rust on a container side wall is almost never a problem. The corrugated walls on a standard ISO container are roughly 2 mm Corten steel, with usable life well past 25 years if the rest of the box stays watertight, and light brown discolouration wire-brushes off to bright steel in seconds. Side walls are where most of the visible brown lives and where most buyers over-react. Wall rust is almost always cosmetic.
Three grades, in increasing severity:
- Surface rust. Light to dark brown across the wall, often following corrugation valleys. Wire brush takes it off in seconds and the steel underneath is bright and intact. Textbook patina. Wire brush, two coats of rust-converter primer, marine-enamel topcoat, and the wall reads as new for another 10 to 15 years. Pricing in our container painting and respray guide.
- Pitting. Surface rust progressed into the steel as visible craters under 1 mm deep. A thumbnail catches on the edge. Remediable with aggressive grind, rust converter, epoxy primer, topcoat. Pitting concentrated in one corrugation valley for 30 cm or more is a flag to inspect for water entry from above.
- Perforation. Rust ate through. Daylight visible, or a screwdriver tip pushes through. Unusual on a 20-year-old container; when we see it, we trace it to a specific upstream water-entry event. Patch-weldable, but raises the question of what else is leaking.
The wire-brush test is honest and quick. Brown comes off cleanly to bright steel: surface rust, fine. Moonscape of pitting or daylight through: more serious wall.
What Should You Check on Container Doors and Gaskets?
On a container door, check five things in order: that both doors swing freely without binding or dropping, the steel gasket channel for scaled rust, the rubber gasket for cracks, the four cam locks and keepers for forced operation, and the door sill for pitting. The door end is the hardest-working part of a shipping container and the highest hit rate for actual deal-breakers. Doors swing on heavy steel hinges, seal against rubber gaskets compressed into machined channels, and rely on cam locks engaging steel keepers. Every interface is a potential rust trap.
The door inspection sequence:
- Open both doors and let them swing. Doors that bind, drop visibly on the hinge, or scrape the sill are showing hinge-pin wear or frame distortion. Either way the frame is no longer square, and a non-square door will leak no matter how good the gasket is.
- Read the gasket channel. Flashlight along the full perimeter from inside the closed door. The U-shaped steel channel is the lowest point of the door frame, so water collects there. Scaled rust, lost paint, or screwdriver-pocket rust in the channel itself means short seal life. Gasket swap is straightforward, channel repair is welding work.
- Inspect the gasket rubber. Pliable, intact, compressing evenly. Cracked, brittle, or split gaskets leak. Gasket replacement is a modest line item on a 20-footer and routine end-of-life on any container older than 15 years.
- Cam lock and keeper alignment. Four cam locks per door rotate to engage steel keepers. Bent cam rods, ovaled keepers, or cam handles that need a hammer to seat are signs of forced operation: the frame is racked.
- Look at the door sill. Horizontal steel ledge the door closes against. Rust collection point of the entire box. Pitting or perforation here is fixable but telegraphs to the gasket. We grind, weld in fresh plate, and re-coat door sills as routine yard work.
Walked the door, then set a hose on the closed container for 15 minutes and watch the inside floor at the door end. Passes: genuinely Wind & Water Tight. Drips: needs gasket work before sale. Grade definitions in our container grades guide.
How Do You Inspect a Container Floor and Cross-Members?
To inspect a container floor, rake a low flashlight across the plywood and push a screwdriver into any soft or stained patch, then crawl underneath on a creeper to read the steel cross-members for scaling rust and bottom-rail perforation. The floor is two layers in one. Visible top: hardwood plywood (apitong or keruing, 28 to 30 mm thick) screwed to a steel sub-frame. Hidden structure: a steel cross-member grid the plywood rests on. Both need a look.
The plywood top: walk the full interior twice, once empty-eyed and once with a flashlight raked low. Raking light reveals cupping, soft spots, and water stains that flat ambient light hides. Push a screwdriver tip into any darker patch, especially the door end, the back wall, or directly under a roof pinhole. A screwdriver that sinks more than 5 mm is into rot, and rot flags a chronic leak above. Plywood replacement is routine yard work for a full 20ft floor, but rot in a container sold as Wind & Water Tight tells you the seller has not actually addressed the leak.
The hidden cross-members are the structural call. Container floors rest on a grid of transverse 4 mm Corten beams running side-to-side between the bottom side rails. Reference: HZ Containers on cross-member construction. Inspection requires looking underneath: containers on our customer row are blocked up on dunnage so you can crawl under on a creeper.
What we look for:
- Surface patina. Acceptable. Cross-members darken with age and the dark grey-brown finish is normal.
- Scaling laminated rust. Active corrosion. Tap with a screwdriver handle. Sound steel rings hard; corroded steel sounds dull and may flex.
- Pitting on the bottom side rail. Highest-loaded, most weather-exposed beam. Pitting acceptable, perforation is structural.
- Forklift gouges. Surface dings are cosmetic. Deep gouges that exposed bare steel and rusted unaddressed for years are structural.
IRS and CEFIC standards (summarized in the HZ container inspection protocol) accept minor patina; structural degradation means part replacement, and rust around the weld joint between cross-member and bottom rail is highest priority because welds concentrate stress.
What Do Corner Castings and the CSC Plate Tell You?
The corner castings tell you whether a container can still be safely lifted and stacked, and the CSC plate tells you its build date, weight ratings, and inspection history. The eight corner castings are the cast-steel knuckles that anchor everything else: spreader-crane lifts, stack-locks, chassis twist-locks. They bear the entire load of a stack. Cast steel rather than rolled Corten, so they corrode on a different schedule.
Corner casting inspection is binary. Two failures only: cracks and perforation. Surface rust on a casting is cosmetic. The casting is 25 to 30 mm thick steel and the outside rust layer is irrelevant to lifting capacity. What is not allowed: a visible crack or a corrosion hole through the wall. Both are dead-stop walk-aways: the casting has lost its load rating, the container can no longer be safely lifted or stacked.
The CSC plate is bolted or welded to the door frame and carries manufacturer, build date, max gross weight, allowable stacking weight, and next inspection date. Layout documented by the Bureau International des Containers; we lay out how we read and verify that data plate in a separate step-by-step on the stamped data plate. Clearly stamped, intact, legible is the baseline. Missing, painted over, or fresh-looking on an old box: ask hard questions before transacting.
What Are the Deal-Breakers That Make Christian Walk Away?
The five rust and corrosion deal-breakers that make Christian walk away from a used container are roof perforation across multiple panels, a cracked corner casting, a soft floor across multiple cross-members, a door frame out of square, and a suspect CSC plate. Most containers I look at pass. A small slice fail outright. The five conditions that trigger walk-away, no negotiation:
- Roof perforation across multiple panels. One pinhole is welding work. Six pinholes across multiple panels tells you the entire roof aged past service life. A full roof replacement is a major line item that turns the deal upside down.
- Cracked corner casting. Even one. Load rating lost, container can no longer be safely lifted or stacked, crack cannot be reliably welded. Replacement is foundry-grade work that costs more than the container is worth.
- Soft floor across multiple cross-members. A localized soft spot is plywood replacement. Screwdriver through in five or six places across multiple cross-member spans is telling you the members below have lost section. Structural walk-away.
- Door frame visibly out of square. If you have to lift the door to engage the cam locks, or cam handles need a sledgehammer, the frame has racked. Will not seal and cannot be rebuilt in field.
- Suspect CSC plate. Missing, freshly applied on an old box, or sticker-fraud inspection date is a red flag for the broader provenance.
Everything else is in the negotiable middle: surface rust, plywood patch, gasket swap, door sill rebuild, paint, lockbox. Those line items get priced into the rental or sale price, and the box moves to the customer row. If you want the full picture of how condition, grade, and these middle-ground fixes fit into a smart second-hand purchase, our broader playbook for choosing a pre-owned unit sets the rust checklist in context.
Local Tip: Watch the Weather When You Inspect
The best day for a yard rust inspection is the day after a hard rain. Pooling shows where the roof and floor really drain. The door gasket either passes the water-entry test or it does not. Cross-members that look dry from above show their actual wet zones underneath. Sunny dry days hide problems that ten minutes of rain make obvious.
What Container Rust Is Fixable, and What Is Not?
Fixable container rust includes surface rust, pitting under 1 mm deep, one or two pinhole perforations, a failed door gasket, plywood floor rot, and cross-member surface patina. Not fixable in the field: multi-panel roof perforation, cracked corner castings, racked door frames, bottom side rail perforation, and cross-member section loss across multiple beams. Once you know the grade, the next question is whether it is worth fixing.
| Condition found | Severity | Fixable in the field? | What it takes |
|---|---|---|---|
| Surface rust on side walls | Cosmetic | Yes | Wire brush, rust-converter primer, marine topcoat |
| Pitting under 1 mm deep | Minor | Yes | Grind to clean steel, metal-loaded epoxy filler, prime, topcoat |
| One or two roof pinholes | Minor | Yes | Patch-weld a Corten or A36 plate square, grind, coat |
| Cracked or split door gasket | Minor | Yes | Strip old rubber, clean channel, install fresh closed-cell EPDM |
| Soft plywood floor patch | Moderate | Yes | Pull screwed sheets, lay fresh marine plywood, re-seal seams |
| Roof perforation across multiple panels | Structural | No | Full roof replacement, not a field repair |
| Cracked corner casting | Structural | No | Load rating lost, casting cannot be reliably welded |
| Door frame racked out of square | Structural | No | Frame cannot be rebuilt in the field, will not seal |
| Cross-member section loss across multiple beams | Structural | No | Floor structure compromised, walk away |
- Surface rust, no pitting. One-day cosmetic. Wire brush or angle grinder with wire wheel, two coats of rust-converter primer (POR-15 or Rust-Oleum Rust Reformer convert ferric oxide to a stable iron tannate), marine-grade enamel topcoat. A modest materials bill plus a day of labour. Reference sequences at OnSite Storage and Universal Containers.
- Pitting under 1 mm deep. Aggressive grind to clean steel, fill the pits with metal-loaded epoxy filler, sand, prime, topcoat. Reads as a repair under raking light but is fully watertight.
- One or two pinhole perforations. Welded patch. Square of fresh Corten or A36 plate, MIG-weld in place, grind smooth, prime, topcoat. A small per-patch charge that scales with how many you find.
- Door gasket failure. Strip the old rubber, clean the channel back to bare steel, install fresh closed-cell EPDM. Inexpensive in parts plus 2 to 4 hours of labour.
- Floor plywood replacement. Pull screwed-down sheets, fresh marine plywood, re-seal seams. A predictable half-day job for a 20ft floor.
- Cross-member surface patina. Acceptable as-is, or wire brush and zinc-rich primer for another 10 years of service life.
The decision rule pulls all of it together: if the total repair budget approaches 40 percent of what a clean used container at the same grade would cost, walk from the rusty one and pay for the clean. When the rust math no longer works at all, a factory-fresh box with original paint and a full service life ahead of it is often the smarter buy, and you can spec a brand-new one-trip unit instead of pouring a repair budget into tired steel.
How Does Van Blanc Run a Rust Inspection at the Brantford Yard?
At the Brantford yard, a Van Blanc rust inspection puts a wire brush and flashlight in the buyer’s hand and walks them down the row in their size and grade, so they read the CSC plates, swing the doors, ladder up for roof pinholes, and pick the exact box that gets delivered. The reason we run 4 yards with 200+ containers on inventory is so buyers can walk the row and inspect rust in person, on the box that will actually get delivered. National franchises ship from a generic pool. You take what the tilt-deck brings. We have not worked that way since 1995.
The standard rust-inspection visit:
- You arrive, we walk you to the row in your size and grade.
- We hand you a wire brush and a flashlight. You walk the row.
- You read CSC plates, open and close doors, climb a step-ladder for the roof, go inside and look up at the ceiling for pinholes.
- You pick the box that reads cleanest for your use case.
- We write paperwork on the box you picked, with the container number tied to the contract.
- The tilt-deck delivers the same container number that is on your contract. No bait-and-switch.
Christian LeBlanc, second-generation operator, 19 years on the yard: “We have customers who drive 90 minutes from Toronto, two hours from Kingston, three hours from Sudbury because they want to read the rust themselves before they pay. The drive pays for itself the first time they see a 4-inch dent in the corner casting of a competitor’s tilt-deck drop on a neighbour’s property. Driving to Brantford and picking your box is the easiest math in our business.”
Once you have read the rust and picked your box, our walkthrough of how a tilt-deck drop works covers what happens on delivery day across Ontario, and our explainer on what actually moves the number covers the size, grade, distance, and steel-market factors behind any quote. Keeping a box watertight after it lands is its own discipline, and our notes on keeping the steel sound year after year walk through the seasonal upkeep that stops surface patina from ever turning into active rust.
Frequently Asked Questions
How do I tell the difference between Corten patina and active rust?
Use the fingernail test. Drag a fingernail across the worst brown patch. Nail stays clean: stable Corten patina, steel underneath sound. Brown scale flakes off and steel underneath shows pitting or fresh oxidation: active rust. Patina is dense and adherent; active rust is porous and laminar.
How many pinholes in a container roof are too many?
One or two pinholes are routine welded patches that add little to the cost of the box. Six or eight in the same panel is the start of a roof-replacement conversation, and a full roof replacement is the kind of line item that tips the math against the container. Pinholes in 3 or more separate panels is a structural concern, not cosmetic.
Is surface rust on the side walls of a used container a problem?
Almost never. Side walls are 2 mm Corten and heavy surface rust comes off with a wire brush to bright steel. Wire brush, rust-converter primer, marine-grade topcoat, and the wall reads as new for 10 to 15 years. The problem is pitting (craters deeper than 1 mm) and perforation (daylight), not the brown discoloration.
What is the most common deal-breaker on a used shipping container inspection?
Door frame distortion. If the door binds, cam handles need force, or the door visibly drops on its hinges, the frame has racked. A racked frame will not seal regardless of gasket condition, and the frame cannot be rebuilt in field. Walk-away.
How do I inspect the floor cross-members on a shipping container?
Look underneath. At our Brantford yards, containers on the customer row are blocked up on dunnage so you can see the cross-member grid. Look for surface patina (acceptable), scaling laminated rust (active), and perforation in the bottom side rail (structural). Tap with a screwdriver handle: sound steel rings hard, corroded steel sounds dull.
Can a cracked corner casting be welded or repaired?
Not reliably. Castings are heavy cast steel and the heat from a structural weld changes the metallurgy in a way that compromises load rating. A cracked casting means the container has lost the certification for crane lifting and stacking. We do not buy containers with cracked castings, and you should not either.
How long does a Wind & Water Tight container last in Ontario weather?
With a properly maintained roof, door gaskets, and paint, a Wind & Water Tight container outlives most outdoor steel structures. We have customers running 1995-build 20-footers from our first delivery year still in clean watertight service in 2026, with two routine repaints in the interval. Service life with maintenance: 25 to 35 years. Without maintenance: 15 to 20 before roof replacement.
What rust repair products do you recommend for a DIY refresh on a used container?
Wire brush or angle grinder with wire wheel, two coats of rust-converter primer (POR-15, Permatex Rust Treatment, or Rust-Oleum Rust Reformer chemically convert ferric oxide into stable iron tannate), topcoat of marine-grade enamel. For pinholes, a welded plate patch is the right answer rather than epoxy filler. Repair-shop pricing for a welded patch is charged per pinhole and stays modest unless the count climbs.
Do you let buyers inspect containers at the Brantford yards before they pay?
Yes, and we are the only Ontario container yard set up for it at this scale. 200+ inventory across our 4 Brantford yards, blocked up for cross-member inspection, mixed grades and sizes. Buyers walk the row, read CSC plates, open and close doors, check for daylight pinholes. The container number on the contract matches the number on the tilt-deck that delivers.
Is a rust patch on a Facebook Marketplace container ever a good deal?
Almost certainly not. The 2025-2026 Marketplace scam pattern prices fake Ontario listings far below the going market rate, with an e-transfer deposit demanded before any yard visit. Photos are stock or reverse-image-searchable to other listings. Any Ontario container priced suspiciously below market from a Facebook seller demanding a deposit before in-person inspection is the scam, not a deal: the bin that looks too cheap to be true is the bin that never arrives.
Ready to price your container?
Tell us the size and your postal code and we’ll send back an honest, all-in number, container, delivery, and placement, usually within 1-3 days. No pressure, no mystery fees.
Family-run in Brantford since 1995 · 200+ containers in stock · 4.9★ across 124+ Google reviews · every box graded by a person, walk it before it lands.
Sources and Further Reading
- Total Materia. Atmospheric Corrosion Resistant Corten Steel. totalmateria.com
- HZ Containers. How Corten Steel Enhances the Durability of Shipping Containers. hz-containers.com
- HZ Containers. Steel Cross-Members of a Shipping Container. hz-containers.com (cross-members)
- HZ Containers. Maintenance and Inspection of Shipping Container Before Stacking. hz-containers.com (inspection)
- Bureau International des Containers. The Container CSC Combined Data Plate Explained. bic-code.org
- YES Containers. Shipping Container Repair: What Can Be Fixed, What It Costs, and When Replacing Makes More Sense. yescontainers.com
- International Organization for Standardization. (2013). ISO 1496-1:2013, Series 1 freight containers – Specification and testing. iso.org
Reach Van Blanc in Brantford
We have been supplying shipping containers across Ontario since 1995, with 200+ container inventory across our 4 Brantford yards and 1-3 day delivery once you have picked your box. Walk the row with us, read CSC plates, open and close doors, climb a step-ladder for the roof, and pick the exact 20-footer or 40-footer that will live on your property before any money changes hands. Cash on delivery, no e-transfer deposits, no bait-and-switch on the container number.
Van Blanc Ent. Inc. 90 Morton Ave E Unit 1B, Brantford, ON N3R 7J7 +1 888-509-6658
Inspecting elsewhere and want a second opinion? Send us photos of the roof, door frame, cross-members, and CSC plate. We will read the rust grade honestly. If the box passes, buy it. If not, we have 200+ alternatives on the yards.
Related Reading
- Used shipping container buying guide (parent hub)
- what to know about container buying
- Container types Canada (grade and size reference)
- Container grades: Wind & Water Tight, Cargo-Worthy, IICL-5
- CSC plate verification guide Ontario
- Container painting and respray Ontario
- Container pricing Canada (rate hub)